1. Field of the Invention
The present invention relates to a webbing winding device for housing a webbing belt for restraining the body of a vehicle occupant by winding the webbing belt on a spool, and in particular to a webbing winding device capable of switching the magnitude of load for absorption in a force limiter mechanism.
2. Related Art
In a webbing winding device described in Japanese Patent Application Laid-Open (JP-A) No. 2007-84042, a first lock mechanism actuates, and an axial direction end side of a torsion shaft coupled to a spool at a length direction intermediate portion is retained by the first lock mechanism, and furthermore, in this state, a second lock mechanism actuates and the axial direction other end side of the torsion shaft is retained by the second lock mechanism. In this state, twisting is generated in the torsion shaft when force to rotate the spool in the pull-out direction exceeds the mechanical strength of the torsion shaft on both sides of the coupling portion to the spool. The spool can rotate in the pull-out direction by the amount of twisting generated in the torsion shaft, and a portion of the force to rotate the spool in the pull-out direction, namely a portion of the tension force on the webbing belt, is absorbed with the twisting deformation of the torsion shaft.
However, if prior to operating the second lock mechanism, engagement of a ring lock pawl configuring the second lock mechanism and a lock ring, configuring the second lock mechanism along with the ring lock pawn, is released, then the second lock mechanism substantially ceases to function. Consequently, in this state, twisting can be induced in the torsion shaft by force to rotate the spool in the pull-out direction exceeding the mechanical strength of the torsion shaft at one end side of the coupling portion.
Accordingly, the configuration described in JP-A No. 2007-84042 can change the magnitude of the so-called force limiter load.
However, in the second lock mechanism of a webbing winding device configured in this manner, when interaction of a wire with a rotation circular plate portion is released, the rotation circular plate portion is pressed by bias force of a compression coil spring provided to a second lock base, and the rotation circular plate rotates relatively with respect to the second lock base. The second lock pawl thereby meshes with internal ratchet teeth of the lock ring, and the second lock mechanism adopts an actuated state.
Due to the above configuration, when assembling the second lock mechanism, the rotation circular plate and the second lock base are assembled in a state in which bias force of the compressed coil spring is being resisted, and the wire also needs to interact with the plate portion of the rotation circular plate, with this resulting in poor manufacturability during assembly.